Contact-less power supply in which power is supplied without power source cords or power transmission cables has been the object of attention in recent years. Conventional schemes for contact-less power supply include, for instance, power supply relying on electromagnetic induction, power supply relying on radio waves, and resonance methods wherein power is supplied relying on electromagnetic field resonance.
For instance, Japanese Patent Application Publication No. 2002-272134 (JP-A-2002-272134), Japanese Patent Application Publication No. 7-337035 (JP-A-7-337035), Japanese Patent Application Publication No. 8-175232 (JP-A-8-175232), Japanese Patent Application Publication No. 2003-250233 (JP-A-2003-250233) and Japanese Patent Application Publication No. 11-225401 (JP-A-11-225401) disclose power supply systems that rely on electromagnetic induction. Japanese Patent Application Publication No. 2009-106136 (JP-A-2009-106136), for instance, discloses a power supply system that relies on resonance.
JP-A-2009-106136 discloses an electric vehicle provided with a power storage device, and discloses a vehicle power supply device for supplying power to the power storage device. The power supply device for vehicles has a high-frequency power driver, a primary coil and a primary self-resonant coil, and the vehicle has a secondary self-resonant coil. The high-frequency power driver converts power received from a power source into high-frequency power. The primary coil receives high-frequency power from the power driver. The primary self-resonant coil is magnetically coupled to the secondary self-resonant coil by magnetic field resonance. The primary self-resonant coil transmits the high-frequency power received from the primary coil to the secondary self-resonant coil. The power received by the secondary self-resonant coil is supplied to the power storage device via a secondary coil and a rectifier that are installed in the vehicle.
Leak electromagnetic fields should ideally be reduced as much as possible in contact-less power supply. In the electromagnetic induction methods disclosed in JP-A-2002-272134, JP-A-7-337035, JP-A-8-175232, JP-A-2003-250233 and JP-A-11-225401, however, the size of the units must be increased in order to reduce leak electromagnetic fields. JP-A-2009-106136 describes the feature of providing a reflection wall for reflecting the magnetic flux that is generated by a primary self-resonant coil, in order to reduce leak electromagnetic fields. However, increasing the number of components that make up the power supply device is a factor that increases costs and that contributes to increasing the size of the power supply device. Thus, further study is required on ways of reducing leak electromagnetic fields in contact-less power supply.